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This talk was given at the 2018 Restore America's Estuary Conference in Long Beach, CA as part of a special session titled "Restoration Perspectives from the Tijuana River National Estuarine Research Reserve." It is based on information from the Tijuana River Valley Historical Ecology Investigation, a report published in 2017.

Though many areas of the binational Tijuana River watershed remain relatively undeveloped, land and water use changes over the past 200 years have resulted in significant ecological impacts, particularly in the more urbanized areas of the lower watershed. Drawing upon a diverse set of historical data, we reconstructed the ecological and hydrogeomorphic conditions of the lower Tijuana River valley prior to major Euro-American modification (ca. 1850) and documented major changes in habitat distribution and physical processes over this time. The river corridor, which was historically dominated by riparian scrub, today instead supports dense stands of riparian forest. The valley bottom surrounding the river corridor, which historically supported extensive seasonal wetlands, has largely been converted to drier habitat types and agricultural uses. The estuary, which historically supported large expanses of salt marsh and mudflat as well as seasonally dry salt flats, has retained much of its former extent and character, but has been altered by increased sediment input and other factors. The new information about the historical landscape presented here is relevant to a number of issues scientists and managers are dealing with today, including the conservation of endangered species, the fate of the valley’s riparian habitats after the recent invasion of invasive shot-hole borer beetles, and the effects on groundwater levels on native plant communities. We will also draw from other historical ecology studies conducted in Southern California to illustrate how the information about the past has been utilized to improve the functioning and resilience of nearby coastal ecosystems.

The Tijuana River Valley Historical Ecology Investigation addresses a regional data gap by reconstructing the landscape and ecosystem characteristics of the river valley prior to the major modifications of the late 19th and 20th centuries. The research presented here, funded by the California State Coastal Conservancy, supplies foundational information at the regional and system scale about how the Tijuana Estuary, River, and valley looked and functioned in the recent past, as well as how they have changed over time. The ultimate goal of this study is to provide a new tool and framework that, in combination with contemporary research and future projections, can support and guide ongoing restoration design, planning, and management efforts in the valley.